Rapid solidification method of calcareous sand

ABSTRACT

Disclosed is a rapid solidification method of calcareous sand, and the method relates to the technical field of a calcareous sand reinforcement in island reef engineering. The specific method is to achieve a rapid solidification of the calcareous sand by applying a zinc sulfate solution to the calcareous sand.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.202210836728.2, filed on Jul. 15, 2022, the contents of which are herebyincorporated by reference.

TECHNICAL FIELD

The application relates to the technical field of calcareous sandreinforcement in island reef engineering, and in particular to a rapidsolidification method of calcareous sand.

BACKGROUND

Calcareous sand particles on coral reefs have internal pores, irregularshapes, and low particle strengths, and are prone to particle breakages.Environments in tropical and subtropical sea areas are harsh, withfrequent storms and frequent precipitations. Especially in an earlystage of a hydraulic fill construction, the calcareous sand particlesare loose and are easy to be lost by a short-term heavy rainfall and atidal scouring. If prevention and control are not carried out, astability of a project is adversely affected. Therefore, the applicationprovides a rapid solidification method of calcareous sand, so as toimprove an anti-erosion performance of the calcareous sand and keep agood engineering stability under harsh natural conditions, so the methodis of great significance to the field of island reef engineeringconstruction.

SUMMARY

Based on the above, the application provides a rapid solidificationmethod of calcareous sand, so as to improve an anti-erosion performanceof the calcareous sand and enable the calcareous sand to maintain a goodengineering stability under harsh natural conditions.

To achieve the above objective, the application provides followingsolutions.

A first technical scheme according to the application is the rapidsolidification method of the calcareous sand, which realizes a rapidsolidification of the calcareous sand by applying a zinc sulfatesolution to the calcareous sand.

In an embodiment, the zinc sulfate solution is a zinc sulfate aqueoussolution; and a concentration of the zinc sulfate aqueous solution is0.4-1.4 mol/L.

In an embodiment, an application mode is spraying; a hydraulic force ina spraying process is 2-5 L/min·m², and a wetting depth of the solutionis not less than 3 cm.

In an actual construction process, the solution concentration and timesof spraying reinforcements may be determined according to an actualsituation.

In an embodiment, the application mode is grouting; and a groutingpressure is 0.5-1.0 MPa.

In an embodiment, the method further includes a step of tamping thecalcareous sand before applying the zinc sulfate solution to thecalcareous sand.

In an embodiment, the method further includes a step of heating afterapplying the zinc sulfate solution to the calcareous sand.

In an embodiment, a heating temperature is 40-60° C. and a duration is0.5-2 hours.

Adding the zinc sulfate solution to the calcareous sand for thereinforcement may be carried out at a room temperature, and heatingafter adding the zinc sulfate solution is to obtain a betterreinforcement effect. In an actual construction process, if a sitetemperature is high, such as a ground temperature may reach above 50degrees in a high temperature weather of the South China Sea, the effectafter a heating treatment may be achieved without an additional heatingoperation.

A second technical scheme of the application is a slope reinforcementmethod of a calcareous sand foundation pit, which realizes thereinforcement by spraying the zinc sulfate solution on a surface of thecalcareous sand foundation pit.

A third technical scheme of the application is a reinforcement methodfor erosion prevention of a calcareous sandy beach, which realizes thereinforcement by spraying the zinc sulfate solution on a surface of thecalcareous sandy beach.

A fourth technical scheme of the application is a reinforcement methodfor preventing a calcareous sand particle loss in a hydraulic fillprocess of an island reef. The zinc sulfate solution reacts chemicallywith the calcareous sand to generate gypsum and zinc carbonate mineralsby spraying the zinc sulfate solution on a calcareous sand surface, andcalcareous sand particles are cemented to reinforce the sand.

Reinforcing the calcareous sand by using the zinc sulfate solution in ahydraulic fill construction may avoid a sand loss caused by a waveerosion in the hydraulic fill construction.

A fifth technical scheme of the application is a reinforcement methodfor a calcareous sand foundation, which realizes a foundationreinforcement by injecting the zinc sulfate solution into the calcareoussand foundation through a pressure grouting.

A technical conception of the application.

More than 90% of a mineral composition of the calcareous sand iscalcite, and a chemical composition of the calcite is calcium carbonate(CaCO₃). Zinc sulfate (ZnSO₄) is selected for a chemical reinforcementof the calcareous sand. Calcium carbonate reacts with zinc sulfate toform two solid substances, smithsonite (ZnCO₃) and gypsum (CaSO₄·2H₂O),so that a generation of some by-products and a harm to the environmentis avoided. Moreover, a strength of the calcareous sand is not weakenedsince an acidic environment is not produced when zinc sulfate reactswith the calcite. A corresponding chemical reaction formula is asfollows:

Zn²⁺+SO₄ ²⁻+CaCO₃→ZnCO₃↓+CaSO₄·2H ₂O↓

According to the above reaction, the calcium sand is treated with thezinc sulfate solution, and Ca²⁺and Zn²⁺exchange in calcite lattices toform smithsonite (ZnCO₃) and gypsum (CaSO₄·2H₂O). In a calcite group,smithsonite is a kind with a high hardness and a high specific gravity,and is insoluble in water and nontoxic. A Mohs hardness of smithsoniteis 4.5, 50% higher than that of calcite with the Mohs hardness of 3, sothe hardness of the calcareous sand particles is improved and particlebreakages are reduced. The other product is gypsum, and gypsum is white,non-toxic and insoluble in water. Smithsonite and gypsum are filled inpores of the calcareous sand particles as cements, forming aninterconnected network structure among the calcareous sand particles,filling the pores of the calcareous sand particles themselves, andmaking the calcareous sand denser.

The application discloses following technical effects.

The method according to the application is simple and convenient tooperate, and may be applied to a site of a hydraulic fill project of theisland reef in the South China Sea. Compared with a microbiologicallyinduced calcite precipitation (MICP) technology, since the MICPtechnology needs a series of complicated operations such as a bacterialinoculation, a culture, a separation and a purification to reinforce thecalcareous sand and is difficult to carry out a large-scale engineeringapplication, the method according to the application is superior to theMICP technology in terms of a feasible engineering application.

The reinforcement effect of the method according to the application isgood, and it may be seen from a uniaxial compression test that thereinforcement effect of the method according to the application isbetter than that of a MICP method.

Urea-hydrolyzing bacteria used by MICP technology to reinforce thecalcareous sand is expensive, while the method according to theapplication only uses the zinc sulfate aqueous solution as thereinforcement liquid, so a cost is low.

The method according to the application has a good environmentaladaptability, and reaction products of the method according to theapplication are smithsonite and gypsum, and both minerals are solidsubstances harmless to the environment and insoluble in water. However,the bacteria used by MICP technology to reinforce the calcareous sandare difficult to adapt to an extreme environment of the South China Seaproject site. The extreme environment may cause a large number ofbacterium to die, thus greatly weakening the reinforcement effect.Moreover, an ecological safety monitoring of microorganisms afterinjecting bacterial solution is also a problem to consider.

The method according to the application has a high reinforcementefficiency, and it may be seen from a penetration test that a surfacestrength reaches a peak value after about 4 hours of the reinforcement,and then the surface strength hardly changes, showing that thereinforcement liquid almost completely reacts after 4 hours of thereaction. At 2 hours, the surface strength may reach 65% of a peakstrength, indicating that at 2 hours, most of the reinforcement liquidhas already participated in a chemical reaction. This result shows thata chemical reaction efficiency of the method according to theapplication is very high, and a possibility and an effect of rescuingthe project in some unexpected situations, such as a seepage preventionand a reinforcement for slope protection before a storm, are improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly explain embodiments of the application ortechnical solutions in the prior art, the following introduces drawingsto be used in the embodiments. Obviously, the drawings in the followingdescription are only some embodiments of the application. For those ofordinary skill in the art, other drawings may be obtained according tothese drawings without any creative efforts.

FIG. 1 shows photos before and after a calcareous sand reinforcement inembodiment 1 of the application, in which a left figure is a photobefore the calcareous sand reinforcement, and a right figure is a photoafter the calcareous sand reinforcement.

FIG. 2 shows scanning election microscope (SEM) images before and aftera calcareous sand reinforcement in embodiment 1 of the application, inwhich the upper left image and the lower left image have a magnificationof 200 times, and the upper right image and the lower right image havethe magnification of 300 times.

FIG. 3 is a photo of a sample prepared in embodiment 2 of theapplication for a uniaxial compression test.

FIG. 4 shows a uniaxial compressive strength test result and acorresponding linear fitting curve of cylindrical samples of reinforcedcalcareous sand under different concentrations of zinc sulfate solutionsin embodiment 2 of the application.

FIG. 5 shows a change rule of a penetration resistance with depth aftera reinforcement of calcareous sand under different concentrations ofzinc sulfate solutions in embodiment 3 of the application, in which,

a represents the change rule of the penetration resistance with depthafter the reinforcement with 0.4 mol/L zinc sulfate solution;

b represents the change rule of the penetration resistance with depthafter the reinforcement with 0.6 mol/L zinc sulfate solution;

c represents the change rule of the penetration resistance with depthafter the reinforcement with 0.8 mol/L zinc sulfate solution;

d represents the change rule of the penetration resistance with depthafter the reinforcement with 1.0 mol/L zinc sulfate solution;

e represents the change rule of the penetration resistance with depthafter the reinforcement with 1.2 mol/L zinc sulfate solution; and

f represents the change rule of the penetration resistance with depthafter the reinforcement with 1.4 mol/L zinc sulfate solution.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments of the application are described indetail. This detailed description should not be taken as a limitation ofthe application, but should be understood as a more detailed descriptionof some aspects, characteristics and embodiments of the application.

It should be understood that terms mentioned in the application are onlyused to describe specific embodiments, and are not used to limit theapplication. In addition, for a numerical range in the application, itshould be understood that each intermediate value between an upper limitand a lower limit of the range is also specifically disclosed. Everysmaller range between any stated value or the intermediate value withinthe stated range and any other stated value or an intermediate valuewithin the stated range is also included in the application. The upperand lower limits of these smaller ranges may be independently includedor excluded from the range.

Unless otherwise stated, all technical and scientific terms used hereinhave the same meanings commonly understood by those of ordinary skill inthe field to which this application relates. Although the applicationonly describes preferred methods and materials, any methods andmaterials similar or equivalent to those described herein may be used inthe practice or testing of the application. All documents mentioned inthis specification are incorporated by a reference to disclose anddescribe the methods and/or materials related to the documents. In caseof a conflict with any incorporated documents, the contents of thisspecification shall prevail.

Without departing from a scope or a spirit of the application, it isobvious to those skilled in the art that many modifications and changesmay be made to the specific embodiments of the present specification.Other embodiments obtained from the description of the application areobvious to the skilled person. The description and the embodiments ofthe application are only exemplary.

As used in this paper, the terms “including”, “including”, “having” and“containing” are all open terms, meaning including but not limited to.

“Parts” mentioned in the application refers to the parts by mass unlessotherwise specified.

Embodiment 1

Calcareous sand is reinforced as follows: 50 milliliters of 0.8 mol/Lzinc sulfate solution is sprayed on a calcareous sand surface, andchanges of micro-morphology after 24 hours are observed.

In this embodiment, photos and scanning election microscope (SEM) imagesbefore and after a calcareous sand reinforcement are shown in FIG. 1(photos) and FIG. 2 (SEM images) respectively. In FIG. 1 , a left figureshows the photo before the calcareous sand reinforcement and a rightfigure shows the photo after the calcareous sand reinforcement. In FIG.2 , an upper left figure and a lower left figure have a magnification of200 times, and an upper right figure and a lower right figure have themagnification of 300 times. FIG. 2 shows that gypsum precipitatesgenerated by a reaction fill internal voids and inter-particle gaps ofcalcareous sand particles, and form cementation between the particles.The cementation between the particles not only makes a porosity of thecalcareous sand decrease significantly, but also makes original angularedges of the calcareous sand particles become smooth, and furtherenlarges a contact surface between the particles, thus reducing a stressconcentration and particle breakages.

The calcareous sand particles are loose and have no cohesive forcebefore the reinforcement, so a particle loss is easy to occur under ascouring action of a water flow. The gypsum is formed between theparticles and in pores of the reinforced calcareous sand, and the looseparticles are cemented; therefore, a strength and a compactness of thereinforced calcareous sand are significantly improved, and thereinforced calcareous sand has an excellent resistance to a water flowerosion. Comparing the calcareous sand before and after thereinforcement (FIG. 1 ), it may be clearly seen that the surface of thereinforced calcareous sand is denser and the pores are filled. After aSEM microscopic test of the reinforced calcareous sand (FIG. 2 ), it maybe observed that the pores on the surfaces of the calcareous sandparticles are all covered by products, and no obvious pores may be seenamong the particles.

Embodiment 2

A uniaxial compressive strength is often used to evaluate areinforcement effect. Mechanical properties of the reinforced calcareoussand are evaluated by a uniaxial compression test and a penetrationtest, and the reinforcement effect is tested and compared with that ofmicrobiologically induced calcite precipitation (MICP) reinforcementtechnology.

In the uniaxial compression test using a reinforcement method accordingto the application: a multifunctional hydraulic prototype is used for asample preparation, and each sample used for the uniaxial compressiontest has a diameter of 50 mm and a height of 100 mm; after the sample(as shown in FIG. 3 ) is made, each sample is put into a small amount ofreinforcement liquid (300 milliliters) for standing for 3 hours, so asto make the reinforcement liquid react with the calcareous sandparticles in the sample; then, the sample is taken out, the surfacemoisture is wiped off, and a sand column sample is put in an oven at 50°C. for curing for about 48 hours until a sample quality does not change;and the uniaxial compression test is conducted at a loading rate of 1.0mm/min until the sample is damaged.

FIG. 4 shows a uniaxial compressive strength curve and a correspondinglinear fitting curve of cylindrical samples of reinforced calcareoussand under different concentrations of zinc sulfate solutions obtainedby the method according to the application. It may be seen that there isa good linear relationship between the concentration of thereinforcement liquid and the uniaxial compressive strength of a sandcolumn; with an increase of the concentration, the uniaxial compressivestrength increases linearly; in the method according to the application,the uniaxial compressive strength of the sand column may reach 2.0 MPawith 0.4 mol/L of the reinforcement liquid, while the maximum uniaxialcompressive strength of the sand column may reach 8.59 MPa with 1.4mol/L of the reinforcement liquid. The results show that thereinforcement effect of the method according to the application isobvious.

Consult related literatures about MICP (microbiologically inducedcalcite precipitation) reinforced calcareous sand ([1] Li Hao, TangChaosheng, Liu Bo, Lyu Chao, Cheng Qing, Shi Bin. Mechanical propertiesof MICP solidified calcareous sand in simulated seawater environment[J]. Journal of Geotechnical Engineering, 2020, 42 (10): 1931-1938; [2]Liu L, Liu H, Stuedlein A W, et al. Strength, stiffness, andmicrostructure characteristics of biocemented calcareous sand [J].Canadian Geotechnical Journal, 2019, 56 (10): 1502-1513. DOI:10.1139/cgj-2018-0007. [3] Dong Bowen, Liu Shiyu, Yu Jin, Xiao Yang, CaiYanyan, Tu Bingxiong. Evaluation of effect of natural seawater oncalcium sand reinforcement based on microbiologically induced calciumcarbonate precipitation [J]. Geotechnical Mechanics, 2021, 42 (4):1104-1114. et al.). Compared with the uniaxial compressive strengths ofthe calcareous sand columns reinforced by the MICP technology, it may beseen that the uniaxial compressive strengths of the calcareous sandcolumns reinforced by the MICP technology are mostly around 2 MPa, andthe uniaxial compressive strengths of the calcareous sand columnsreinforced by the method according to the application are much higherthan the uniaxial compressive strengths of the calcareous sand columnsreinforced by the MICP.

It is worth noting that a period of a sand column reinforcement by themethod according to the application is only 3 hours, that is, the sandcolumn is soaked with the reinforcement liquid, and a volume of thereinforcement liquid used for soaking is only 300 milliliters, while areinforcing process of a MICP method is roughly as follows: a groutingliquid includes a bacterial solution, a fixing liquid and a mineralizingsolution which are in a stable period after 48 hours of culture;effective components in the mineralizing solution are urea and calciumchloride, and their molar ratio is 1:1; during a grouting reinforcement,100 milliliters of the bacterial solution (about 1.5 times the volume ofa sand column) is injected first, 10 milliliters of the fixing liquid(0.05 mol/L CaCl2) is injected after an interval of 6 hours, and thenthe mineralizing solution is injected after the interval of 6 hours tocomplete a reinforcement treatment for one day. In order to ensure amineralization effect, a duration of reinforcing the calcareous sandwith the MICP is set to 5 days.

It may be seen that the period of reinforcing the calcareous sand by theMICP method is much longer than the period by the method according tothe application, so the MICP method may not be used for an engineeringrescue. The process of the MICP method is complicated and is far lesssimple and practical than the method according to this application.Moreover, the effect of the reinforced calcareous sand by the MICPmethod is not as good as that of the method according to theapplication.

Embodiment 3

The penetration test of the calcareous sand after the surfacereinforcement is carried out to study the reinforcement effect of thereinforcement liquid with different concentrations and an increasing lawof a surface strength with time. The reinforcement method of thecalcareous sand is as follows: site reinforcement conditions aresimulated in a laboratory. Calcareous sand samples are put into a roundcontainer, and a surface reinforcement test simulates the reinforcementof the calcareous sand surfaces by spraying and moistening. The testsand is the original graded calcareous sand taken from an island reef inNansha Islands. Oversized gravel blocks are removed, and the calcareoussand is not treated at all, so as to keep its original properties, so asto simulate an actual engineering reinforcement environment of theisland reef in the South China Sea. The concentrations of the zincsulfate solutions are set to 0.4 mol/L, 0.6 mol/L, 0.8 mol/L, 1.0 mol/L,1.2 mol/L and 1.4 mol/L. The reinforcement liquids are evenly sprayed onthe calcareous sand surfaces by a spraying process. The volumes of thereinforcement liquids used in all reinforcement tests are the same(about 80 g), an immersion depth is 3 cm, and a reaction environmenttemperature is kept at 27° C. After the reinforcement, the surfacestrength is tested by a micro-penetrometer. A diameter of a probe needleis 2.0 mm and a penetration rate is 5 mm/min.

FIG. 5 shows a change rule of a penetration resistance with depth. Itmay be seen that the penetration resistance increases rapidly with apenetration depth, and then enters a relatively stable stage, andgradually decreases, and finally fluctuates in a lower range and tendsto be stable. This shows that the reinforcement effect is mainlyconcentrated on a shallow surface, because the calcareous sand at asurface layer is fully contacted with the reinforcement liquid under anaction of spraying, so a stronger particle cementation is formed, whilethe calcareous sand at a lower layer is less contacted with thereinforcement liquid, so the cementation is weak. It may be seen thatwhen the strength tends to be stable, the penetration strength isdiscrete to some extent, because the reinforcement liquid contacted bythe lower calcareous sand is infiltrated by the reinforcement liquidsprayed on the surface along the pores between the particles. Therefore,due to an irregularity of a particle arrangement, the amount of thereinforcement liquid contacted by each place in the lower layer isdifferent, so a cementation degree of each place in a lower part isuneven. However, an overall trend of the stable penetration resistanceincreases with time.

In order to show the reinforcement effect more intuitively, pure water(about 80 g) with the same volume as the reinforcement liquid used inthe penetration test is added into the sample, and then the penetrationtest is carried out. The pure water is only added to make the sampleachieve a same wetting effect as that of the reinforcement liquid, butdoes not cement the sample. From test curves, it may be seen that apenetration curve of the sample only added with the pure water is quitedifferent from that of the sample using the reinforcement liquid. Withthe increase of a penetration depth, the penetration resistanceincreases approximately linearly, and there is no situation similar to arapid rise of the penetration resistance at the initial stage of thepenetration after the use of reinforcement fluid.

Indoor tests of embodiments 1-3 prove an excellent solidification effectof the method according to the application on the calcareous sand,indicating that the method according to the application may be used in ahydraulic fill project of the island reef in the South China Sea.

In a practical application, 0.6-1.4 mol/L reinforcement liquid (zincsulfate aqueous solution) may be selected for a slope surfacereinforcement, and a reinforcement depth is not less than 3 cm. It isrecommended to use a high concentration zinc sulfate solution for aslope stabilization in case of a sudden rainstorm. The reinforcementliquid with a high concentration may be selected for a foundationreinforcement. Because of a complex environment of a project site, anaddition amount and reinforcement times should be determined accordingto actual project requirements.

The reinforcement liquid (zinc sulfate aqueous solution) is preparedwith the pure water, and the contact between the solution and vulnerableparts of a body should be avoided during a preparation process.Considering a rapid response and the obvious reinforcement effect ofthis method, for some projects that need the surface reinforcements,such as a slope reinforcement of a calcareous sand foundation pit, ascouring reinforcement of a beach and the reinforcement for a particleloss prevention during a hydraulic fill process of the island reef, itis recommended to use a spraying device and adopt a spraying process(the solution concentration is 0.6-1.4 mol/L, and a spraying amountshould not be less than a pore volume of the calcareous sand to bereinforced), and a hydraulic power may be controlled at 2-5 L/min·m²during the spraying reinforcement process. Moreover, The solution shouldbe sprayed evenly, and a recommended wetting depth of the solution isabout 5 cm. The solution concentration and the times of the sprayingreinforcement may be determined according to the actual situation. For afoundation reinforcement, a conventional pressure grouting method may beused, a grouting pressure is 0.5-1.0 MPa, and the reinforcement liquidis injected into the calcareous sand.

In an embodiment, the surface layer of the calcareous sand foundationsprayed with the reinforcement liquid is compacted by a vibratoryroller, so that a compaction degree of the calcareous sand reaches morethan 80%. Then, the spraying reinforcement of 2-5 L/min·m² is carriedout again (the concentration of the solution is 0.6-1.4 mol/L, and aspray amount should not be less than the pore volume of the calcareoussand to be reinforced). After a completion, a weight (50 kg/m²) iscovered on the reinforced sand body, and the reaction process ismaintained, so that the foundation may reach a consolidated and densestate.

In an embodiment, the reinforced sand body is covered with the weight(50 kg/m²), and the compacted calcareous sand body is heated after areaction process is kept compact for about 1 day. The temperature iscontrolled at 40-60° C. and the duration is 0.5-2 hours. A site workingcondition is complex, when there is no corresponding equipment, thesolidification may be carried out in a high temperature and little rainweather to promote a conversion of internal dihydrate gypsum intohemihydrate gypsum further improving the reinforcement effect (in fact,a site ground temperature may reach more than 50 degrees in a hightemperature weather of the South China Sea, and the effect after theheating treatment may be achieved without additional heating operation).The sand body shall not be trampled or disturbed during and after thereinforcement, so as not to damage the cementation between theparticles.

The zinc sulfate used in this method is completely soluble in water.This means that toxicological effects in an aquatic environment must beconsidered. The zinc sulfate solution has no irritation to a skin, andmay be used as a nutrient for animals with zinc deficiency, a feedadditive for animal husbandry, and a zinc fertilizer for crops. The zincsulfate solution reacts with the calcareous sand to produce smithsoniteand gypsum. The two minerals are solid substances harmless to theenvironment and insoluble in water. Zn²⁺is considered harmless, and evenused as a dietary supplement in some cases. Meanwhile, there are a lotof Zn²⁺and SO₄ ²⁻in seawater, so a proper amount of zinc sulfatesolution is harmless to a marine environment. Moreover, the reactionefficiency of this method is very high, and a reinforcement reaction maybe completed within a few hours, so a proper operation does not causeenvironmental and ecological problems.

The above-mentioned embodiments only describe preferred modes of theapplication, but do not limit the scope of the application. On a premiseof not departing from a design spirit of the application, all kinds ofmodifications and improvements made by ordinary technicians in the fieldto the technical scheme of the application shall fall within the scopeof protection determined by claims of the application.

What is claimed is:
 1. A rapid solidification method of calcareous sand,wherein a rapid solidification of the calcareous sand is realized byapplying a zinc sulfate solution to the calcareous sand.
 2. The rapidsolidification method of the calcareous sand according to claim 1,wherein the zinc sulfate solution is a zinc sulfate aqueous solution;and a concentration of the zinc sulfate aqueous solution is 0.4-1.4mol/L.
 3. The rapid solidification method of the calcareous sandaccording to claim 1, wherein an application mode is spraying; ahydraulic force in a spraying process is 2-5 L/min·m², and a wettingdepth of the solution is not less than 3 cm.
 4. The rapid solidificationmethod of the calcareous sand according to claim 1, wherein theapplication mode is grouting; and a grouting pressure is 0.5-1.0 MPa. 5.The rapid solidification method of the calcareous sand according toclaim 1, further comprising a step of tamping the calcareous sand beforeapplying the zinc sulfate solution to the calcareous sand.
 6. The rapidsolidification method of the calcareous sand according to claim 5,further comprising a step of heating after applying the zinc sulfatesolution to the calcareous sand; and a heating temperature is 40-60° C.and a duration is 0.5-2 hours.
 7. A slope reinforcement method for acalcareous sand foundation pit and beach erosion prevention, wherein thereinforcement is realized by spraying zinc sulfate solutions on surfacesof the calcareous sand foundation pit and calcareous sandy beach.
 8. Areinforcement method for preventing a calcareous sand particle loss in ahydraulic fill process of an island reef and a calcareous sandfoundation, wherein the reinforcement is realized by spraying a zincsulfate solution on a surface of the calcareous sand foundation to formgypsum and zinc carbonate cement.